The present invention relates, in general, to apparatus and methods for joining together wooden, plastic and particle board workpieces and, more particularly, relates to apparatus suitable for forming obliquely oriented counterbores and fastener receiving bores to allow toe-fastening together of two members.
There are many applications in joinery in which two members must be secured together by fasteners in such a way that the fastening elements are not visible from the outside surfaces of the resulting structure. In U.S. Pat. No. 3,496,974, for example, a stepped drill bit is disclosed which is suitable for forming a counterbore and fastener receiving bore in the back side of a wooden member proximate the edge thereof to permit the formation of a face frame. The counterbore and the screw receiving bore are both formed at a relatively shallow angle (or oblique angle if measured from the drill axis in the direction of advancement of the drill) with respect to the back surface of the member being drilled proximate an edge thereof. A screw positioned in the screw receiving bore hole and extends outwardly of the edge of the member to permit threading of the screw into a second member. As shown in U.S. Pat. No. 3,496,974, the members are oriented in substantially the same plane and joined together in abutting relation. It is also possible to use this same toe-fastening approach to join one member in a perpendicular orientation to another member.
U.S. Pat. No. 3,675,312 discloses an alternative apparatus and process for joining together two members in perpendicular relation to each other. This approach also employs an obliquely oriented tool access hole and a large counterbore which is drilled into the edge of the member which will carry the screw. An annular insert is then adhesively secured in the counterbore with the screw in the central bore of the insert, and the access opening is used to drive the screw into the second member.
It is very difficult, however, to drill a counterbore at a shallow or oblique angle with respect to a workpiece. The drill will tend to wander, more particularly it will be deflected toward a parallel orientation with the surface as it enters. The bore that is cut is very often ragged and characterized by chipping. For particle board and hardboard, as well as very hard lumber, drilling at a shallow angle, even with jigs or fixtures, is almost impossible. Similarly, for plastics having low friction surfaces it is extremely difficult to start a stepped drill having a configuration as shown in U.S. Pat. No. 3,496,974.
The approach shown in U.S. Pat. No. 3,675,312 has the disadvantage of requiring a separate insert piece which must be secured by a separate process, as well as a specialized tool. Moreover, the time required to form a joint is undesirably long. Other even more complex face-framing apparatus can be seen in U.S. Pat. Nos. 1,335,544 and 1,602,658.